Residents in Langtoft, Peterborough have been filling bags with clothes and other items to raise money for the East Anglian Air Ambulance.
The bags were handed out by World UK Trading, which was due to collect the donations once the bags had been filled.
However, residents have been reporting that another firm has been collecting the bags, and not sending them onto the charity.
The police are currently investigating the matter.
Executive director of East Anglian Air Ambulance Simon Gray said: "While the police investigation continues, residents who have yet to have their bag collected are asked to ensure that the collector has the correct identification.
"Donors with concerns can contact World UK Trading's helpline on 0845 2702887 or e-mail them at pauline@worlduk tradingltd.com
"The company will then work with them to ensure their donation is safely received by the East Anglian Air Ambulance.
"All information received will be treated confidentially, and may help ensure that no further bags are misappropriated."